Portable manually-operated grease guns are extremely useful in many situations, especially by farmers and others who work around machinery in the field as well as vehicle owners who wish to lubricate their own vehicles. These hand-held grease guns are easy to use, and with the development and availability of replaceable and disposal grease cartridges, the undesirable job of refilling the gun housing with grease is eliminated. With the use of the replaceable and disposable cartridges, a spring biased plunger discharges the grease from the cartridge into an area where a manually operated mechanism will force the grease through a discharge nozzle. A manually operated grease gun of this type is shown in U.S. Pat. No. 3,780,830. A similar hand operated grease gun which does not use replaceable cartridges is shown in U.S. Pat. No. 1,659,950.
Although the manually operated grease guns employ force multiplying mechanisms, the effort required to operate the mechanism to discharge the grease frequently requires considerable effort, and makes the use of these guns difficult in some instances. Moreover, some vehicles and equipment require considerable pressure to force the grease into the grease fitting.
There have been developed electrically supplied power-operated caulking guns such as those shown in U.S. Pat. Nos. 4,264,021 and 4,024,994. However, these guns can be used only where electric power is available, therefore rendering them useless for farmers in the field, for example. Battery operated power tools are currently known and used, such tools employing rechargeable batteries so that they can be used in the field. However, there is a need for a simple and inexpensive grease gun that is portable and battery-powered and which is relatively inexpensive so as to be available to a wide variety of users.